Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$109.39	13.159%	$123.7846	$123.78	$123.80	$123.80
Purchase #2	$227.95	11.410%	$253.9591	$253.96	$253.95	$254.00
Purchase #3	$171.96	3.387%	$177.7843	$177.78	$177.80	$177.80
Purchase #4	$101.50	6.337%	$107.9321	$107.93	$107.95	$107.90
Purchase #5	$24.58	5.336%	$25.8916	$25.89	$25.90	$25.90
Purchase #6	$142.72	7.213%	$153.0144	$153.01	$153.00	$153.00
Purchase #7	$148.90	6.457%	$158.5145	$158.51	$158.50	$158.50
7 purchase totals =	$927.00		$1,000.8806	$1,000.86	$1,000.90	$1,000.90